There are many applications in which a transfer of torque is required. In many devices, it is desirable to transmit pure torque through a machine component with high torsional stiffness in a very controlled and repeatable manner.
For example, testing machines, such as orthopedic device wear testing machines, will often have a component to which torque is applied repeatedly. After a number of cycles in which torque is transmitted to the orthopedic device implant, numbering in the millions, for example, wearing of the orthopedic device implant test specimen is determined. It is critical in such testing machines that the torque be transmitted with little deflection related error and be repeatable. In an orthopedic device implant wear testing machine, for example, a plurality of test stations are provided in which test specimens are tested. A precise and consistently repeatable torque transmission must be applied to each of the test specimens over the millions of test cycles so that each of the test specimens are subjected to the same wear conditions. Otherwise, the validity of the testing will be in question.
In certain devices, such as in orthopedic device wear test machines, a torque transfer transmission to provide precise force and motion control and rigid torque transfer along with axial loading. One such orthopedic device wear testing machine is a spinal implant wear test machine. In such a machine, for example, axial loading is provided on the spinal implant under test, and a torque is also applied to the test specimen. In such devices, it is desirable to provide high torsional stiffness with little deflection related error, while at the same time providing low axial stiffness so that cross-talk is not seen at the load cell.